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Vaso-Occlusive Crises (VOCs) in patients with SCD cause acute and chronic morbidity including disabling pain, hospitalizations, missed school and work, end-organ damage, and early mortality. VOC prophylaxis, while beneficial, does not address the disabling pain and morbidity of breakthrough VOC events that still occur. E-selectin upregulation on vascular endothelium leads to leukocyte trapping, activation and aggregation and is a critical driver of acute VOC (Morikis et al, Blood 2017). Rivipansel, a pan-selectin inhibitor with potent activity against E-selectin, prevents interaction between leukocytes and vascular endothelium (Morikis et al, Blood 2017) and increases blood flow by reducing cell-cell aggregates and vascular occlusion in a SCD mouse model (Chang et al, Blood 2010). A phase 2 study of rivipansel in VOC demonstrated shorter hospital stays and reduced opioid use (Telen et al Blood, 2015). The RESET trial (NCT02187003) was a phase 3, randomized, double-blind, placebo-controlled, study of the efficacy and safety of rivipansel for VOC requiring hospitalization. Three hundred forty-five patients (204 patients ≥18 and 141 patients 6-17 years of age) were randomized to an intravenous rivipansel loading dose, followed by up to 14 additional doses Q 12 hr, or placebo, in addition to standard care. Overall, 320 were treated: 162 with rivipansel, 158 with placebo. Pre-treatment variables were well balanced, including concomitant hydroxyurea use, genotype, chronic opioid use, gender, and country. The primary endpoint was time to readiness for discharge (TTRFD), and key secondary endpoints were time to discharge (TTD), time to discontinuation of IV opioids (TTDIVO), and cumulative IV opioid use (CIVO). Hazard ratios or ratios of medians, and confidence intervals were calculated for each. Both study arms had comparable baseline soluble E-selectin (sE-sel) levels and inflammatory/coagulation biomarkers. Median sE-sel in the rivipansel group decreased by 59% from baseline after a loading dose while increasing by 9% in the placebo group. Although the RESET study did not show statistically significant improvements in outcomes for the total population, additional analysis demonstrated that rivipansel treatment within 26.4 hr of pain onset (earliest quartile of duration of VOC until treatment) reduced median TTRFD by 56.3 hrs (from 122.0 to 65.7 hrs), reduced median TTD by 41.5 hrs (from 112.8 to 71.3 hrs), and reduced median TTDIVO by 50.5 hrs (from 104.0 to 53.5 hrs), compared to placebo. There was also a consistent trend for lower hazard ratios for rivipansel treatment earlier during VOC (up to ~36 hr from onset) for all endpoints (Figure 1). Pediatric subjects (6-17 yrs, n = 141) were 41% of patients treated in the RESET trial (71 in rivipansel arm, 70 in placebo arm). As in the overall population the observed benefit with rivipansel in pediatric subjects depended on duration of VOC prior to treatment. Children 6-17 yrs of age treated with rivipansel within 30 hrs of onset of VOC experienced reduction in median TTRFD by 29.3 hrs (from 94.1 to 64.8 hrs), reduction in median TTD by 23.2 hrs (from 92.8 to 69.6 hrs), and reduction in median TTDIVO by 15.4 hrs (from 68.9 to 53.5 hrs). Early treatment with rivipansel decreased median TTRFD by more than one day and led to more children ready for discharge by 24, 48, and 72 hrs, compared to patients receiving placebo (Table 1). Additionally, pain scale assessments (VAS and Faces scale) showed a substantial reduction in the time to first clinically meaningful reduction in pain (data not shown). Thus, the hazard ratios for the efficacy endpoints favored early rivipansel treatment over placebo in the overall population and the pediatric population (Table 2). Summary: Rivipansel administered early in VOC results in clinically meaningful benefit for adults and children with SCD, shortening IV opioid use and hospital stay. Biomarker data confirm on-target effect, suggesting that the diminishing effect of later rivipansel treatment results from downstream pathophysiology. These findings suggest the utility of early treatment to shorten or interrupt acute VOCs, analogous to thrombolysis for heart attack or stroke. This could change the VOC treatment paradigm from deferral of hospitalization to one of early intervention to reduce length of hospitalization and IV opioid requirement, relieve VOC symptoms, and possibly mitigate end-organ damage from tissue ischemia. Disclosures Dampier: Merck: Research Funding; Hudson Publishing Company: Consultancy, Research Funding; CLS Behring: Consultancy, Other: DSMB Chair; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Micelle Biopharma: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Cyclerion: Consultancy, Other: DSMB Chair; Novartis: Research Funding. Telen:GlycoMimetics Inc.: Consultancy; Forma Therapeutics: Research Funding; CSL Behring: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Wun:GlycoMimetics, Inc.: Consultancy; Pfizer, Inc.: Other: Steering Committee for clinical study, Research Funding. Smith:Incyte: Other: Investigator; Pfizer: Consultancy; Ironwood: Consultancy; Novo Nordisk: Consultancy; Imara: Research Funding; Shire: Research Funding; NHLBI: Research Funding; Patient-Centered Outcomes Research Institute: Other: Investigator, Research Funding; Health Resources and Services Administration: Other: Investigator, Research Funding; Shire, Inc.: Other: Investigator, Research Funding; Global Blood Therapeutics, Inc.: Consultancy, Research Funding; Novartis, Inc.: Consultancy, Other: Investigator, Research Funding; Emmaeus Pharmaceuticals, Inc.: Consultancy; GlycoMimetics, Inc.: Consultancy. Brown:Global Blood Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Forma Therapeutics, Inc,: Research Funding; Imara, Inc.: Consultancy, Research Funding; Novartis, Inc.: Consultancy, Research Funding. Desai:Pfizer, Inc.: Membership on an entity's Board of Directors or advisory committees, Research Funding; GBT, Inc.: Membership on an entity's Board of Directors or advisory committees, Research Funding; Ironwood Pharmaceuticals, Inc.: Membership on an entity's Board of Directors or advisory committees; Rockpointe Continuing Medical Education Company: Consultancy. El Rassi:Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Cyclerion: Research Funding; Pfizer: Research Funding; Global Blood Therapeutics: Membership on an entity's Board of Directors or advisory committees; Bluebird bio: Membership on an entity's Board of Directors or advisory committees. Kanter:Wells Fargo: Honoraria; Medscape: Honoraria; Guidepoint Global: Honoraria; NHLBI Sickle Cell Advisory Board: Membership on an entity's Board of Directors or advisory committees; SCDAA Medical and Research Advisory Board: Membership on an entity's Board of Directors or advisory committees; AGIOS: Membership on an entity's Board of Directors or advisory committees; BEAM: Membership on an entity's Board of Directors or advisory committees; Jeffries: Honoraria; GLG: Honoraria; Sanofi: Consultancy; bluebird bio, inc: Consultancy, Honoraria; Novartis: Consultancy; Cowen: Honoraria. Pastore:Pfizer: Honoraria. Rothman:Pfizer: Consultancy, Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Agios Pharmaceuticals: Honoraria, Research Funding. Readett:Pfizer, Inc.: Current Employment. Lozier:GlycoMimetics, Inc.: Current Employment, Current equity holder in publicly-traded company. Magnani:GlycoMimetics, Inc.: Current Employment, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties. Thackray:GlycoMimetics, Inc.: Current Employment. Hassell:Pfizer, Inc.: Other: RESET Study Steering Committee; Pfizer, Inc.: Research Funding.

Background: Pyruvate Kinase (PK) deficiency is caused by mutations in the PKLR gene leading to chronic hereditary non-spherocytic hemolytic anemia. Diagnostic evaluation can be challenging with falsely normal PK enzyme activity levels in chronically transfused patients, in those with profound reticulocytosis, or in patients with mutations with unusual biochemical properties. Genetic testing can also be complex, as up to 20% of affected patients have new PKLR variants and up to 10% of patients have variants not routinely detected through exon sequencing. The phenotypic spectrum is broad, and biomarkers of clinical severity would be helpful for both prognosis and monitoring. Aims: To describe the correlation of PK enzyme activity, red cell PK (PK-R) protein level, and red cell metabolites [adenosine triphosphate (ATP), 2,3-diphosphoglycerate (2,3-DPG)] with clinical phenotype. To estimate the sensitivity of PK enzyme activity to diagnose PK deficiency in a cohort of patients with genetically confirmed PK deficiency. Methods: Blood samples were collected from a subset of 41 patients enrolled in the PK Deficiency Natural History Study, all with two confirmed PKLR mutations and no red cell transfusions for ≥3 months prior to the blood sample. PK and hexokinase (HK) enzyme activity testing were performed using standard biochemical assays (Beutler 1985) at the Stanford Red Blood Cell Special Studies Laboratory (normal ranges: PK activity: 3.2-6.5 EU/gm Hb, HK activity: 0.14-0.37 EU/gm Hb). Baseline PK-R protein was quantitated by antibody-based capture and detection using a Meso Scale assay and the signal normalized to a control sample without PK deficiency. ATP and 2,3-DPG concentrations (μg/ml) in blood were analyzed using qualified tandem mass spectrometry methods and then normalized for individual hemoglobin (Hb) values (ATP and 2,3-DPG concentrations were converted to g/dL and divided by Hb (g/dL)). Spearman correlation coefficients were calculated to estimate the correlation between continuous variables, and Wilcoxon rank-sum testing was used to assess the association of continuous and binary variables. Results: The median age was 25.3 years (range 1.4-60.4) and 80% of patients were splenectomized (Table). The mean PK enzyme activity level was 1.1 EU/gm Hb with 90% (37/41) of patients with low PK activity. Normal PK activity was observed in 4 patients, 3 of whom had high HK activity and a low PK/HK ratio (normal mean PK/HK ratio 15.6, range: 8.7-22.5), with a sensitivity of 98% (40/41) when both PK activity and PK/HK ratio were used together. There were no correlations between PK enzyme activity and clinical severity indicators, including transfusion status (p=0.3), splenectomy status (p=0.4), or post-splenectomy Hb (r=0.109). Normalized ATP levels were significantly correlated with normalized 2,3-DPG levels (r=0.93) and higher in ever transfused (median=0.0022, range=0.0011-0.0029) compared with never transfused patients (median=0.0012 , range=0.0008-0.0020), (p=0.004). PK-R protein level was inversely correlated with the total number of transfusions prior to enrollment (r= -0.53) and was higher in never transfused (median=40.1%, range=9.8-73.9%) compared with ever transfused patients (median=7.7%, range=0.4%-15.1%), (p=0.0014). Conclusions: In this cohort with a molecularly confirmed diagnosis, PK deficiency was detected by enzyme testing with 98% sensitivity by utilizing both the PK activity and the PK/HK ratio. Although these assays cannot distinguish between heterozygotes and affected patients, the combination of PK activity and the PK/HK ratio is useful as a screening test to determine which patients require genetic testing. There was no correlation between PK enzyme activity and clinical phenotype. PK-R protein and ATP levels were inversely correlated with clinical severity and may be a helpful marker of disease phenotype. Disclosures Al-Samkari: Agios: Consultancy, Research Funding; Moderna: Consultancy; Dova: Consultancy, Research Funding. Glader:Agios Pharmaceuticals, Inc: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Chonat:Alexion: Other: advisory board; Agios Pharmaceuticals, Inc.: Other: advisory board. Thompson:bluebird bio, Inc.: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Baxalta: Research Funding. Kuo:Agios: Consultancy; Alexion: Consultancy, Honoraria; Apellis: Consultancy; Bioverativ: Other: Data Safety Monitoring Board; Bluebird Bio: Consultancy; Celgene: Consultancy; Novartis: Consultancy, Honoraria; Pfizer: Consultancy. Ravindranath:Agios Pharmaceuticals, Inc.: Other: I am site PI on several Agios-sponsored studies, Research Funding. Rothman:Pfizer: Consultancy, Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Agios: Honoraria, Research Funding. Kwiatkowski:Celgene: Consultancy; Terumo: Research Funding; Imara: Consultancy; Apopharma: Research Funding; Novartis: Research Funding; bluebird bio, Inc.: Consultancy, Research Funding; Agios: Consultancy. Kung:Agios Pharmaceuticals, Inc: Employment, Other: Stakeholder. Kosinski:Agios Pharmaceuticals, Inc: Employment, Other: Stakeholder. London:United Therapeutics: Consultancy; ArQule, Inc: Consultancy. Grace:Novartis: Research Funding; Agios Pharmaceuticals, Inc: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding.

Introduction: Pyruvate kinase (PK) deficiency causes a defect in the glycolytic pathway, leading to a hereditary hemolytic anemia. Management is supportive and consists of splenectomy, transfusions, and chelation therapy. Aim: To better understand the comorbidity and complication profile of adults with PK deficiency, and the extent to which transfusion frequency contributes, the objectives of this study were to (1) quantify the prevalence of comorbidities and complications according to transfusion history and (2) compare the types and rates of select comorbidities and complications with the general population. Methods: Data were obtained from the enrollment survey of the PK Deficiency Natural History Study (NHS), a longitudinal, retrospective and prospective cohort study in which clinical, laboratory, transfusion, and radiologic data were collected; all participants were confirmed to have 2 mutations in the PKLR gene. Patients (n=122) were eligible for this analysis if they were ≥18 years of age and had sufficient data on transfusion history to enable classification into 1 of 3 cohorts: "Ever Regularly Transfused" (ERT, defined as ≥6 transfusions in any 12-month period), "Never Regularly Transfused" (NRT, defined as having ≥1 lifetime transfusion but never having >4 transfusions in any 12-month period), or "Never Transfused" (NT). To contextualize the findings, the frequencies of select conditions were compared with an age- and gender-matched cohort of individuals from the insured, general US population who did not have any hemolytic anemia diagnoses and had ≥5 years of continuous enrollment in the Truven MarketScan administrative claims database. The NHS reported lifetime prevalence rates, whereas rates obtained from the MarketScan data were based on diagnosis and procedure codes over varying look-back periods; therefore, to minimize bias, we limited PK deficiency vs. general population comparisons to (1) chronic conditions that require lifetime management and would thus still be recorded in claims data years after initial diagnosis, and/or (2) conditions for which a diagnosis/procedure date was available in the NHS and could be matched in time to the average 8-year look-back period for the general population. Frequencies were compared across mutually exclusive cohorts using Fisher's exact 2-tailed tests of significance. Results: ERT (n=65), NRT (n=30), and NT patients (n=27) had a mean age of 34.2, 39.5, and 37.2 years at enrollment, respectively (not significant [ns]), with 46.2%, 56.7%, and 59.3%, respectively, being male (ns). ERT patients trended toward being more likely than NT patients to be Amish and have the homozygous R479H splice variant (30.8% vs 11.1% [p=0.064]) but were significantly less likely to have a missense/missense PKLR genotype (32.3% vs 70.4% [p=0.001]). Compared with the general population, patients with PK deficiency had significantly higher rates of splenectomy, cholecystectomy, osteoporosis, liver cirrhosis, pulmonary hypertension, and current prophylactic antibiotic and anticoagulant use (Table). Rates of splenectomy, cholecystectomy, and osteoporosis were significantly higher in patients with PK deficiency, regardless of transfusion cohort, and both ERT and NRT patients had significantly higher rates of liver cirrhosis than individuals from the general population. A gradient was seen across transfusion cohorts for other conditions. Notably, 83.1% of ERT patients, 50.0% of NRT patients, and 25.9% of NT patients had a history of liver iron overload. ERT patients were also significantly more likely than NRT and NT patients to have had a splenectomy, cholecystectomy, and/or thrombosis, and to currently use prophylactic antibiotics. Findings were consistent when the analysis was restricted to non-Amish patients with PK deficiency. Conclusions: Patients with PK deficiency have higher rates of select comorbidities and complications than age- and gender-matched individuals who do not have PK deficiency. Even patients with PK deficiency who have never been transfused are at increased risk of complications of the disease and its treatment. Disclosures Boscoe: Agios Pharmaceuticals, Inc.: Employment, Equity Ownership. Yan:Agios Pharmaceuticals, Inc.: Consultancy. Hedgeman:IBM Watson Health: Employment. van Beers:Agios Pharmaceuticals, Inc.: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Research Funding; Pfizer: Research Funding; RR Mechatronics: Research Funding. Al-Samkari:Agios: Consultancy, Research Funding; Dova: Consultancy, Research Funding; Moderna: Consultancy. Barcellini:Incyte: Consultancy; Alexion: Consultancy, Speakers Bureau; Agios Pharmaceuticals, Inc.: Consultancy; Novartis: Speakers Bureau; Apellis: Consultancy; bioverativ: Consultancy. Eber:Agios Pharmaceuticals, Inc.: Consultancy. Glader:Agios Pharmaceuticals, Inc: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Chonat:Alexion: Other: advisory board; Agios Pharmaceuticals, Inc.: Other: advisory board. Rothman:Agios: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding. Kuo:Agios: Consultancy; Alexion: Consultancy, Honoraria; Apellis: Consultancy; Bioverativ: Other: Data Safety Monitoring Board; Bluebird Bio: Consultancy; Celgene: Consultancy; Novartis: Consultancy, Honoraria; Pfizer: Consultancy. Kwiatkowski:Agios: Consultancy; bluebird bio, Inc.: Consultancy, Research Funding; Imara: Consultancy; Apopharma: Research Funding; Novartis: Research Funding; Celgene: Consultancy; Terumo: Research Funding. Ravindranath:Agios Pharmaceuticals, Inc.: Other: I am site PI on several Agios-sponsored studies, Research Funding. Neufeld:Octapharma, Shire Pharmaceuticals (Baxalta), Novo Nordisk, Celgene, NHLBI/NIH: Research Funding; Octapharma, Agios, Acceleron, Grifols, Pfizer, CSL Behring, Shire Pharmaceuticals (Baxalta), Novo Nordisk, ApoPharma, Genentech, Novartis, Bayer Healthcare: Consultancy; Octapharma: Other: study investigator, NuProtect study (Octapharma-sponsored). Holzhauer:Agios Pharmaceuticals, Inc.: Consultancy. Verhovsek:Sickle Cell Disease Association of Canada: Membership on an entity's Board of Directors or advisory committees, Research Funding; Canadian Haemoglobinopathy Association: Membership on an entity's Board of Directors or advisory committees; Vertex: Consultancy; Sickle Cell Awareness Group of Ontario: Membership on an entity's Board of Directors or advisory committees. Kunz:Novartis: Membership on an entity's Board of Directors or advisory committees. Sheth:Apopharma: Other: Clinical trial DSMB; Celgene: Consultancy; CRSPR/Vertex: Other: Clinical Trial Steering committee. Despotovic:Novartis: Research Funding; Dova: Honoraria. Grace:Agios Pharmaceuticals, Inc: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Research Funding.

Background: Pyruvate kinase deficiency (PKD) is the most common cause of chronic hereditary non-spherocytic hemolytic anemia. The spectrum of disease in PKD is broad, ranging from an incidentally discovered mild anemia to a severe transfusion-dependent anemia. Splenectomy partially ameliorates the anemia and reduces the transfusion burden in the majority of patients. Because hemoglobin poorly correlates with symptoms in PKD, transfusion requirements are typically used clinically to classify disease severity with those who are regularly transfused despite splenectomy recognized as the most severely affected subgroup. Aim: To compare demographics, complications, and laboratory results between the most severely-affected PKD patients (those that are splenectomized and regularly transfused) with non-regularly transfused splenectomized PKD patients. Methods: After ethics committee approval, patients were enrolled on the PKD Natural History Study, a prospective 30 site international study. All patients had molecularly confirmed PKD. Only splenectomized patients were included in the analysis. Transfusion frequency was observed over a 3-year period. Patients were divided into two groups based on transfusion frequency: the severe phenotype group was defined as those who receive regular transfusions (≥6 discrete red cell transfusion episodes per year) and the control group did not receive regular transfusions. Phenotype stability over the 3-year period was also assessed. Results: 154 splenectomized patients with PKD were included: 30 patients in the severe PKD phenotype group and 124 patients in the comparison PKD group. Results of the analysis comparing the two groups are described in the Table. Severely affected patients were more likely to be female (77% versus 51%, p=0.013), older at the time of splenectomy (median age: 5 versus 3.6, p=0.011), have iron overload (93% vs. 51%, p Conclusions: Patients with PKD who are regularly transfused despite splenectomy appeared to have similar rates of PKD-associated complications (except for iron overload) and similar relevant laboratory values and genotypes when compared to those who are not regularly transfused after splenectomy. The similarity observed between severe phenotype patients and comparison patients with PKD may result from a protective effect of transfusion (e.g. reduction of bone fractures and extramedullary hematopoiesis) or could suggest transfusion-dependence is an artificial signifier of disease severity, reflective of provider practices and patient symptoms rather than an actual distinct phenotype. Transfusion requirements in severe PKD appear to fluctuate significantly over time. Disclosures Al-Samkari: Dova: Consultancy, Research Funding; Agios: Consultancy, Research Funding; Moderna: Consultancy. van Beers:RR Mechatronics: Research Funding; Agios Pharmaceuticals, Inc.: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Research Funding; Pfizer: Research Funding. Barcellini:Agios: Consultancy, Other: Advisory board; Apellis: Consultancy; Incyte: Consultancy, Other: Advisory board; Bioverativ: Consultancy, Other: Advisory board; Novartis: Research Funding, Speakers Bureau; Alexion: Consultancy, Research Funding, Speakers Bureau. Eber:Agios Pharmaceuticals, Inc.: Consultancy. Glader:Agios Pharmaceuticals, Inc: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Chonat:Alexion: Other: advisory board; Agios Pharmaceuticals, Inc.: Other: advisory board. Kuo:Pfizer: Consultancy; Novartis: Consultancy, Honoraria; Celgene: Consultancy; Agios: Consultancy; Alexion: Consultancy, Honoraria; Apellis: Consultancy; Bioverativ: Other: Data Safety Monitoring Board; Bluebird Bio: Consultancy. Despotovic:Dova: Honoraria; Novartis: Research Funding; Amgen: Research Funding. Kwiatkowski:Celgene: Consultancy; Terumo: Research Funding; Apopharma: Research Funding; bluebird bio, Inc.: Consultancy, Research Funding; Agios: Consultancy; Imara: Consultancy; Novartis: Research Funding. Thompson:Baxalta: Research Funding; Novartis: Consultancy, Research Funding; bluebird bio, Inc.: Consultancy, Research Funding; Celgene: Consultancy, Research Funding. Ravindranath:Agios Pharmaceuticals, Inc.: Other: I am site PI on several Agios-sponsored studies, Research Funding. Rothman:Pfizer: Consultancy, Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Agios: Honoraria, Research Funding. Verhovsek:Sickle Cell Awareness Group of Ontario: Membership on an entity's Board of Directors or advisory committees; Sickle Cell Disease Association of Canada: Membership on an entity's Board of Directors or advisory committees, Research Funding; Canadian Haemoglobinopathy Association: Membership on an entity's Board of Directors or advisory committees; Vertex: Consultancy. Kunz:Novartis: Membership on an entity's Board of Directors or advisory committees. Sheth:CRSPR/Vertex: Other: Clinical Trial Steering committee; Apopharma: Other: Clinical trial DSMB; Celgene: Consultancy. London:United Therapeutics: Consultancy; ArQule, Inc: Consultancy. Grace:Novartis: Research Funding; Agios Pharmaceuticals, Inc: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding.

Introduction: The incidence of venous thromboembolism (VTE) in hospitalized pediatric patients is increasing secondary to the growing medical complexity of pediatric patients and the increasing use of central venous catheters. Pediatric patients diagnosed with VTE have up to 2% mortality associated directly with their thromboses. While incidence, risk factor identification and preventive strategies are well established in hospitalized adults, this information is limited in the pediatric population. There are currently no standardized VTE risk screening tools or thromboprophylaxis guidelines for children at Duke Children's Hospital. The incidence of hospital acquired VTE (HA-VTE), as well as their associated risk factors were investigated in a retrospective review. Methods: Medical records of pediatric patients hospitalized at Duke Children's Hospital during June 2018 through November 2018 were reviewed. The EPIC SlicerDicer tool was used to identify patients with ICD-10 diagnoses codes related to thrombosis or treated with anticoagulants. Included patients were diagnosed with HA-VTE during their hospitalization or within 14 days of discharge. Data collected included demographics, thrombosis characteristics, family history, mobility, and acute or chronic co-morbid conditions. The characteristics of the study population were described by median (with 25th and 75th percentiles) for continuous variables and frequencies (with percentages) for binary or categorical variables. Results: Out of 4,176 total pediatric admissions to all units of Duke Children's Hospital (ages 0-18.99 years) during the inclusion timeframe, 33 VTE events were identified. The incidence of VTE events per 1000 patient days was 0.98. The complete patient and VTE event characteristics are listed in Tables 1 and 2. The median age of patients with VTE events was 0.4 years. Of the identified cohort, 73% had an associated central venous line (CVL). Neonates with congenital cardiac disease comprised the majority of the cohort. Other common patient characteristics observed in this cohort included impaired mobility, recent major surgery, and recent mechanical ventilation. Of the 33 VTE diagnoses, 70% received therapeutic anticoagulation with enoxaparin or unfractionated heparin. Only 2 patients (8%) received prophylactic anticoagulation prior to their diagnosis of VTE. Conclusions: The retrospective review of HA-VTE events at Duke Children's Hospital identified that the majority of the events occurred in neonates with congenital cardiac disease and the presence of CVLs. It was also noted that there was no standardization among the use of anticoagulation agents that were initiated for treatment of VTE. Furthermore, few patients received VTE prophylaxis during the hospitalization. A limitation of this review was that it was retrospective and the documentation of family history of thrombosis was inconsistent. It is also possible that several VTE events were missed due to inadequate ICD-10 coding. Based on the results of this review, there is a need to implement a risk stratification tool and develop standardized recommendations of VTE prophylaxis and treatments for pediatric patients admitted to Duke Children's Hospital. There is an additional quality improvement phase of this project and the goal is to implement a risk calculator that is based on information learned from the retrospective review. Ultimately, this risk calculator will help to decrease the incidence of VTE events at Duke Children's Hospital. Disclosures Rothman: Agios: Honoraria, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding; Novartis: Honoraria, Research Funding.

Background: Pyruvate Kinase (PK) deficiency is the most common enzyme defect of the glycolytic pathway causing hereditary non-spherocytic hemolytic anemia. Patients have a broad phenotypic spectrum, ranging from mild anemia to transfusion dependence, and there is wide variation in transfusion practices and decisions about splenectomy. No prior studies have reported on the use of validated health related quality of life (HRQoL) measures in this population. Aim: To describe patient reported outcomes including general HRQoL and fatigue in adults with PK deficiency and the correlation with clinical and laboratory features. Methods: Patients were enrolled on the PK Deficiency Natural History Study, a prospective 30 site international study. All patients had molecularly confirmed PK deficiency. Adults (n=132), ages ≥18 years, completed the EuroQol-5D (high index equivalent to better QoL), PROMIS Fatigue Short Form 7a (high scores equivalent to higher fatigue), and the Functional Assessment of Cancer Therapy-Anemia (FACT-An, high scores equivalent to less fatigue) surveys at enrollment and annually. Timing of administration was convenience based. Survey data were analyzed according to proprietary scoring guidelines. Tests of association were performed using Fisher's exact test (categorical) and Wilcoxon rank sum test (continuous). Regular transfusions were defined as ≥6 transfusions in 12 months. Genotypes were grouped as two missense mutations (M/M), one missense/one non-missense (M/NM), or two non-missense mutations (NM/NM)); non-missense included deletions or other drastic variants. The minimal important difference (MID) for the FACT-An has been reported as 7 points (Cella et al, J Pain Symptom Manage 2002). P-values Results: At enrollment, 128 adults completed the FACT-An with a median total score of 156 (IQR 122-190). Patients receiving regular transfusions reported significantly lower FACT-An scores than those who were not regularly transfused (median 129 vs 156, p=0.004) with significantly lower scores for physical, emotional, and functional well-being and anemia sub-scores (Table). This difference also surpassed the MID. However, non- regularly transfused patients with hemoglobin (Hb) 1000 ng/dL or chelation), higher number of lifetime transfusions, and two missense mutations. Females reported significantly lower scores than males (median 143 vs. 160, p=0.006) with significantly lower anemia sub-scores (p=0.0009). FACT-An surveys completed at the one year follow-up time point validated these findings. EuroQol-5D scores (n=124) at enrollment were similar to the healthy population (median PK deficiency index score 0.88; healthy population index mean 0.88, Shaw et al, Medical Care 2005). No significant differences were found by Hb level, splenectomy status, transfusion status, or genotype group. The median PROMIS fatigue T score (n=66) was 52.1 (IQR 40.5-63.7). Similar to the FACT-An survey data, PROMIS fatigue scores were significantly worse in patients who were regularly transfused (67.0 vs 52.4, p=0.02). PROMIS fatigue scores were also significantly worse in patients ≥40 years old (p=0.05) and females (p=0.01). Conclusions: Using the FACT-An and PROMIS Fatigue measures, patients with PK deficiency who are regularly transfused report significantly more fatigue and worse HRQoL compared with those who are not transfused. Important differences were also seen by iron status and mutation group using the FACT-An. Patients report similar fatigue levels regardless of Hb level, which suggests that symptoms, rather than Hb value alone, should be factored into clinical decision making. In contrast to anemia related HRQoL scores, overall HRQoL scores using validated generic measures in patients with PK deficiency show no differences compared with the healthy population, suggesting that disease-specific measures may better detect the effects of PK deficiency on HRQoL. Disclosures Van Beers: Agios Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Glader:Agios Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Chonat:Agios Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees. Despotovic:AmGen: Research Funding; Novartis: Research Funding; Sanofi: Consultancy. Kwiatkowski:bluebird bio: Consultancy, Honoraria, Research Funding; Agios Pharmaceuticals: Consultancy, Research Funding; Novartis: Research Funding; Apopharma: Research Funding; Terumo: Research Funding. Thompson:La Jolla Pharmaceutical: Research Funding; Baxalta/Shire: Research Funding; Novartis: Research Funding; Celgene: Research Funding; bluebird bio: Consultancy, Research Funding; Biomarin: Research Funding; Amgen: Research Funding. Newburger:TransCytos LLC: Consultancy; Janssen Research & Development, LLC: Consultancy, Honoraria; X4 Pharmaceutics: Consultancy, Honoraria. Ravindranath:AGIOS: Other: Site Investigator for Pyruvate Kinase Deficiency. Sheth:Terumo Corporation: Research Funding; Novartis: Research Funding; La Jolla Pharmaceutical Company: Research Funding; Celgene Corporation: Consultancy, Research Funding; Bluebird Bio: Consultancy. Grace:Agios Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Agios Pharmaceuticals: Research Funding; Agios Pharmaceuticals: Consultancy.

Background: The impact of second line therapies on health related quality of life (HRQoL) and fatigue in pediatric patients with ITP is not well studied. Objective: To describe the impact of second line therapies on HRQoL and fatigue in North American pediatric patients with ITP. Methods: A longitudinal observational cohort of 120 children with ITP starting second line treatments was enrolled from 2013-2015 at 21 ICON centers. Enrollment requirements included age 1-17y and starting a second line treatment (not IVIG, corticosteroids or anti-D immunoglobulin) as monotherapy. HRQoL (Kids ITP Tool - KIT) and fatigue (Hockenberry Fatigue Scale - FS) surveys were completed prior to starting treatment (baseline) and 1 and 12 months after starting treatment by patient/caregiver. KIT is scored from 0 (worst) to 100 (best), and the FS scores were re-scaled so that 0 is no fatigue and 100 is highest fatigue. At the same time points as the patient/caregiver surveys, physicians assessed the perceived effect of treatment on patient HRQoL using a 7-point scale. ANOVA was used to compare the baseline means of the treatment groups. This study specifically compared change from baseline to 1 month in the KIT and FS using paired t-tests within each treatment group. The 12 month timepoint was not used in the paired analysis of individual treatments due to attrition between 1 and 12 months. Results: The median age at enrollment was 11.3 y (1.2-17.8), and 16% (19/120) had newly diagnosed ITP, 31% (37/120) had persistent ITP, and 53% (64/120) had chronic ITP. The median number of prior treatments was 3 (range: 1-9). Fifty-eight (48%) patients had received at least one prior second line treatment. Treatments selected for second line treatment included: rituximab (n=43), romiplostim (n=31), eltrombopag (n=20), oral immunosuppressants (n=19), splenectomy (n=4), and dapsone (n=3). The child and parent proxy KIT scores significantly improved on rituximab (p As previously described, at enrollment, physicians reported that ITP had impacted the patients' HRQoL severely in 15%, significantly in 45%, moderately in 38%, and almost not at all in 3%. Physicians reported that HRQoL improved in 68% (range: 64-75%) of patients while on treatment from baseline to 1 month with no significant difference by treatment group (p=0.46). The physician's assessment of the patient's baseline HRQoL significantly correlated with the child and parent proxy KIT report (p At enrollment, the median FS-Child score (n=54) was 18.5 (range 0-85), the median FS-Adolescent score (n=42) was 20.2 (0-73), and the median FS-Parent (n= 100) score was 35 (7-81). One month FS-Child improved for those who were treated with rituximab (p=0.03); there was no significant change in fatigue on the other treatments. One month FS-Parent significantly improved for those treated with rituximab (p=0.015) and eltrombopag (p=0.009). Conclusions: In this pediatric cohort, all second line treatments appear to significantly improve HRQoL in ITP. Rituximab had the greatest impact in decreasing fatigue at one month. Physician assessment of patient HRQoL did not correlate well with patient assessment after treatment was started, suggesting there may be challenges in ascertaining the effect of treatment on HRQoL. Future analysis of ICON1 will consider the impact of treatment on HRQoL and fatigue while also accounting for the treatment effect on bleeding and platelet count. Disclosures Grace: Agios: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Klaassen: Amgen: Consultancy; Hoffman-La Roche LTD: Consultancy; Octapharma: Honoraria; Baxalta: Honoraria; Biogen Canada LTD: Consultancy; Agios Pharmaceuticals: Consultancy. Despotovic: Sanofi: Consultancy; Schell Cooley LLP: Other: Expert witness. Bussel: Protalex: Membership on an entity's Board of Directors or advisory committees, Research Funding; Momenta: Membership on an entity's Board of Directors or advisory committees; Rigel: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Membership on an entity's Board of Directors or advisory committees, Research Funding. Rothman: Pfizer: Consultancy; Agios Pharmaceuticals: Honoraria. Haley: Genentech: Honoraria; Baxalta: Honoraria; CSL Behring: Honoraria. Neufeld: Octapharma: Consultancy, Honoraria; Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees. Lambert: Educational Concepts in Medicine: Honoraria; Novartis: Honoraria; AstraZeneca: Research Funding.

Background: Venous thromboembolism (VTE) is an uncommon but clinically significant postoperative complication in children. Incidence of VTE in pediatric patients ranges from 34-58 per 10,000 hospitalized children1. Due to rarity of these events, there is limited information about the factors predisposing children to VTE after surgery. We queried a national surgical database to identify risks and outcomes associated with VTE in pediatric surgical patients. Methods: The National Surgical Quality Improvement Program-Pediatric (NSQIP) is a prospectively collected database that records pediatric surgical information, surgical approaches, and 30 day patient outcomes. The database was queried for the years 2012-2013 to identify pediatric patients (age < 18) who had received surgical intervention and were diagnosed with postoperative VTE. Because of their separate coding in NSQIP, we defined VTE as including venous thromboembolism, or pulmonary embolism (PE) diagnosed radiographically within 30 days of operation. To reduce non-random differences between patients we used propensity scores based on age, sex, race, BMI, and ASA classification to match patients in a 1:2 ratio using the nearest neighbor method. Using univariate and multivariate analysis, we identified preoperative risk factors associated with VTE. Results: In total, 130 patients were identified who developed VTE postoperatively (VTE n=122, PE n=7, BOTH PE + VTE n= 1) from this database of 114,395 patients. There were 104 patients with VTE that also had complete entries and were subsequently analyzed in this study. Surgical specialties treating patients in this analysis included cardiothoracic surgery, general surgery, neurosurgery, orthopedic surgery, otolaryngology, plastic surgery, and urology. Eighty-one unique operative CPT codes were identified for patients with VTE. Patients who developed VTE had increased operative time, anesthesia time, and total length of stay (all p < 0.001). Multivariate analysis demonstrated that pneumonia (odds ratio [OR] 1.73, 95% confidence interval [CI] 1.3 - 2.29), Central Line Associated Bloodstream Infection (CLABSI) (OR 1.69, 95% CI 1.18 - 2.42), sepsis (OR 1.47, 95% CI 1.18 - 1.82), septic shock (OR 1.36, 95% CI 1.06 - 1.75), and current solid or hematologic malignancy or active treatment of malignancy (OR 1.30, 95% CI 1.08 - 1.58) were all statistically significant risk factors associated with development of VTE (all p < 0.05). Conclusions: Postoperative VTE risk is significantly increased in children with malignancy or severe infections. Further research is needed to understand the mechanism between malignancy, systemic inflammation, and VTE risk in children. These findings may help to identify patients in need of prophylactic treatment in order to reduce postoperative thrombotic risk in pediatric patients. References: 1. Raffini L, Huang YS, Witmer C, Feudtner C. Dramatic increase in venous thromboembolism in children's hospitals in the United States from 2001 to 2007. Pediatrics. 2009;124(4):1001-1008. Disclosures No relevant conflicts of interest to declare.

Background: The indications for treating children with immune thrombocytopenia (ITP) remain controversial. A valid and reliable bleeding assessment tool could assist in objectively quantifying bleeding and influence treatment decisions. Both the ITP Bleeding Score (IBLS) and the ITP-Bleeding Assessment Tool (BAT) have been developed to assess bleeding severity in ITP. The IBLS scores bleeding severity using an 11-item tool with grading from 0 to 2 and the 18-item BAT grades from 0 to 3 or 4. The BAT includes some types of bleeding not represented on the IBLS, such has intramuscular hematomas. To date, no data describe how these two measures compare when measuring bleeding associated with ITP. Objective: To describe and compare bleeding as assessed by both the IBLS and BAT and to correlate bleeding severity with platelet counts in a cohort of children with ITP. Methods: A longitudinal observational cohort of children ages >1 and < 18 years with ITP, were enrolled from 2013-2015 in the Pediatric ITP Consortium of North America ICON1 trial. All children were enrolled prior to starting a new second line monotherapy (not IVIG, steroids or anti-D). At enrollment, bleeding was assessed using the IBLS in all children. A subset of children also underwent a BAT assessment. Grades of bleeding were described and compared between tools and agreement in grading was assessed. Severity was correlated with platelet count using Spearman's correlation calculation. Results: 118 children were enrolled from 21 ICON centers. 54% had chronic ITP and the median age was 11.4y (range 1.2-17.8). The mean platelet count was 28 x 109/l (SD 57) and 88% had a baseline platelet count of Conclusion: The IBLS and BAT were similarly effective at identifying bleeding symptoms, although neither tool showed strong correlation with the platelet count. There were moderate correlations noted between skin bleeding scores and platelet counts for both tools. A major limitation of this comparison is the different definitions of bleeding severity between the two measures. For sites where the items were more detailed, agreement declined (i.e. adding specificity reduced generalizability). While no patients in our cohort exhibited significant grade 3 or 4 bleeding outside of skin findings, we conclude that in the setting of clinical trials, the ability to capture very severe bleeding might be an important distinction that supports using the more complicated BAT, but for clinical practice, a simplified assessment such as the IBLS may suffice. Disclosures Grace: Agios Pharmaceuticals: Other: Scientific Advisor, Research Funding. Neufeld:Novartis: Consultancy. Bussel:Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; UpToDate: Patents & Royalties; Protalex: Membership on an entity's Board of Directors or advisory committees, Research Funding; Genzyme: Research Funding; Ligand: Membership on an entity's Board of Directors or advisory committees, Research Funding; Symphogen: Membership on an entity's Board of Directors or advisory committees; Rigel Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Shionogi: Membership on an entity's Board of Directors or advisory committees; Sysmex: Research Funding; Momenta Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Immunomedics: Research Funding; Eisai: Membership on an entity's Board of Directors or advisory committees, Research Funding; Boehringer Ingelheim: Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Cangene: Research Funding; Prophylix Pharma: Membership on an entity's Board of Directors or advisory committees, Research Funding; GSK: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Physicians Education Resource: Speakers Bureau; BiologicTx: Research Funding. Haley:CSL Behring: Honoraria; Baxalta: Membership on an entity's Board of Directors or advisory committees. Thompson:Celgene: Research Funding; ApoPharma: Consultancy, Membership on an entity's Board of Directors or advisory committees; Mast: Research Funding; Amgen: Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Research Funding; Amgen: Research Funding; Baxalta (now part of Shire): Research Funding; bluebird bio: Consultancy, Research Funding; Baxalta (now part of Shire): Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; bluebird bio: Consultancy, Research Funding; Mast: Research Funding; ApoPharma: Consultancy, Membership on an entity's Board of Directors or advisory committees; Eli Lily: Research Funding; Eli Lily: Research Funding.

Background: Decision-making in selecting second-line therapies for pediatric patients with immune thrombocytopenia (ITP) has not been studied. Using data collected from physicians experienced in treating ITP, we developed a conceptual model of factors that informed treatment choice. This study was a component of ICON1, a prospective, observational, longitudinal cohort study of second line treatments for childhood ITP performed by the Pediatric ITP Consortium of North America (ICON). Methods: Physicians who enrolled patients in ICON1 were asked to rank the top three reasons they chose a specific treatment so as to weight each factor. Those choices that were ranked 1, 2, or 3 were weighted to develop a propensity scored decisional model. In other questions, physicians were asked about all factors that may have influenced decisions to begin a particular second line therapy and this data was then used to examine additional factors that influenced therapy choices and to compare between therapies. Results: ICON1 enrolled 118 patients; 101 had primary ITP and 53 were receiving their first second line therapy. The majority of physicians in the study saw eleven or more patients per year, and the time since completion of fellowship ranged from 1 to 44 years (mean 12.5 (SD 11)). The most important factors guiding treatment decisions in propensity weighted modeling were "patient preference factors": patient/parental preference (40%), and treatment-related factors: possibility of remission (38%), side effect profile (36%), efficacy (27%), long-term toxicity (33%), and ease of administration (30%). Physician factors, such as experience and adhering to published guidelines, rarely influenced decision-making with only 2% of physicians giving published guidelines as a reason for choice of therapy, and there being no difference in choice based on years since fellowship or experience in treating ITP patients. However, 28% of physicians stated their comfort level with a treatment strongly influenced their choice. Additionally, 38% of physicians did not endorse any patient clinical factors (e.g. frequency of bleeding, expected compliance, response to other therapies, age, comorbidities) as key in their decision-making. Health system factors, such as insurance approval or distance from the closest medical center, rarely influenced treatment choice. Treatments could be categorized into five groups: oral immunosuppressive agents, rituximab, romiplostim, eltrombopag or splenectomy. A significant determinant of choosing splenectomy or rituximab was the "possibility of long-term remission" (p Conclusions: This first analysis of physician decision making regarding second line therapies shows that patient preference and physician perception of treatment characteristics (efficacy, side effects, possibility of long term remission) are primary drivers of physician choice in contrast to guidelines, clinical characteristics and health system factors. Future comparative effectiveness studies are necessary to better inform patient and physician choice. Disclosures Lambert: Novartis: Consultancy. Grace:Agios Pharmaceuticals: Other: Scientific Advisor, Research Funding. Bussel:Cangene: Research Funding; GSK: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Ligand: Membership on an entity's Board of Directors or advisory committees, Research Funding; Sysmex: Research Funding; Symphogen: Membership on an entity's Board of Directors or advisory committees; BiologicTx: Research Funding; Shionogi: Membership on an entity's Board of Directors or advisory committees; Physicians Education Resource: Speakers Bureau; Protalex: Membership on an entity's Board of Directors or advisory committees, Research Funding; Immunomedics: Research Funding; Rigel Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Boehringer Ingelheim: Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; UpToDate: Patents & Royalties; Momenta Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Prophylix Pharma: Membership on an entity's Board of Directors or advisory committees, Research Funding; Genzyme: Research Funding; Eisai: Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Haley:Baxalta: Membership on an entity's Board of Directors or advisory committees; CSL Behring: Honoraria. Neufeld:Novartis: Consultancy.

Introduction: The multicenter phase 3 randomized clinical trial TCD With Transfusions Changing to Hydroxyurea (TWiTCH, NCT01425307) investigated whether hydroxyurea could maintain TCD velocities and prevent stroke in children with sickle cell anemia and abnormal TCD velocities. The trial was stopped early after reaching the primary endpoint, when the average TCD velocity in the alternative (hydroxyurea) arm was found to be non-inferior and even slightly better (138 versus 143 cm/sec) than the standard (transfusion) arm. A planned secondary analysis was to determine the variation in serial TCD velocity measurements for individual study participants, to document the normal TCD velocity fluctuations that occur and to inform the need for frequent TCD evaluations in this clinical setting. Methods: All TCD examinations collected in TWiTCH were analyzed for the maximum time-averaged mean velocity (TAMV) measured in the main intracranial arteries. TCD studies were performed by certified examiners using identical non-imaging instruments, no more than one week before a scheduled transfusion or phlebotomy procedure. Measurements on the index side, defined as the cerebral hemisphere with the higher mean arterial velocity at baseline assessment, were used for these statistical analyses. TCD values were analyzed according to four phases of the trial: (1) screening with three monthly TCD examinations performed at Weeks -8, -4, and 0 before randomization; (2) initial treatment period (hydroxyurea dose escalation with overlap transfusions or transfusions only) with three quarterly TCD measurements at Weeks 12, 24, and 36; (3) steady-state treatment period (hydroxyurea only or transfusions only) with four quarterly TCD measurements at Weeks 48, 60, 72, and 84; and (4) study exit with three monthly TCD examinations performed at Weeks 96, 100, and 104 or during the accelerated close-out period. The within-patient variance and standard deviation of the TAMV values were found using a linear mixed model, which was calculated using SAS Version 9.3. Results: TAMV measurements on the index side from 1458 TCD examinations on 121 randomized patients formed the overall dataset. TAMV values ≥170 cm/sec were identified in 140 measurements on 40 children (9.6% of TCD values) and exceeded 200 cm/sec in 1.8% of examinations (26 values, 8 children) during the study treatment phase. The within-patient TCD variation, representing fluctuation of repeated TCD measurements in the same study participant, was 12.0 cm/sec for the entire cohort during the initial screening phase (363 TCD measurements). In the initial treatment phase, TCD variation in the hydroxyurea arm (180 values, 60 children) was 10.5 cm/sec, similar to 10.2 cm/sec on the transfusion arm (183 values, 61 children). In the steady-state treatment phase, the TCD variation in the hydroxyurea arm was 10.2 cm/sec (207 values, 57 children), compared to 12.3 cm/sec on the transfusion arm (212 values, 58 children). In the final exit phase, TCD variation in the hydroxyurea arm was 9.8 cm/sec (155 values, 58 children), similar to 10.2 cm/sec on the standard arm (155 values, 57 children). TCD variation was greater with higher baseline TCD velocity and shorter transfusion duration, but was not affected by age or gender. For example, participants with baseline TCD velocity of Conclusions: The TWiTCH trial provides prospective data regarding the biological variation in serial TCD values that occurs in children with previous abnormal TCD examinations but no severe vasculopathy. The observed within-patient variation in TCD velocities was consistently 10-14 cm/sec, with higher variation observed in children with higher baseline TCD velocities. This fluctuation can be expected with serial TCD examinations and should be considered before making treatment decisions based on a single TCD measurement. Since comparison of entry and exit TCD values in the TWiTCH trial documented that hydroxyurea at maximum tolerated dose was non-inferior to transfusions, frequent TCD examinations may not be warranted. Disclosures Ware: Bayer Pharmaceuticals: Consultancy; Addmedica: Research Funding; Global Blood Therapeutics: Consultancy; Bristol Myers Squibb: Research Funding; Biomedomics: Research Funding; Nova Laboratories: Consultancy. Heeney:Eli Lilly and Company: Research Funding; Pfizer: Research Funding; Sancilio and Company: Consultancy, Research Funding. Thompson:Baxalta (now part of Shire): Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Mast: Research Funding; Eli Lily: Research Funding; Celgene: Research Funding; Amgen: Research Funding; ApoPharma: Consultancy, Membership on an entity's Board of Directors or advisory committees; bluebird bio: Consultancy, Research Funding.

Background: PKD causes a defect in glycolysis resulting in a hereditary non-spherocytic hemolytic anemia. The prevalence of iron overload is not well described for PKD. Aim: We aim to describe the demographic features and prevalence of iron overload in transfusion dependent and transfusion independent patients with PKD. Methods: Between March 2014 and April 2016, 203 patients enrolled on the PKD Natural History Study at 29 IRB approved sites. All patients were confirmed to have two compound heterozygous or homozygous mutations in the PKLR gene. Children < 1 year of age (n=9) were excluded from this analysis, because elevated ferritin levels are less reliably related to iron overload. Patients were designated with iron overload at the time of enrollment if the plasma ferritin was >1000 ng/mL or the patient was on chelation therapy at any time during the prior 12 months. Patients were designated with having had iron overload if a MRI ever showed liver iron content (LIC) >3 mg/g dry weight or if they had ever received chelation therapy. Tests of association were performed using Fisher's exact test (categorical) and Wilcoxon rank sum test (continuous). Linear associations between variables were measured by Pearson correlation coefficient. P-values Results: Of the 194 patients, 111 (57%) were adults ≥18 years and 83 (43%) were children. The median age of enrollment was 20.6 y (range: 1.3-69.9). Splenectomy had been performed in 65% (126/194). Screening ferritin levels were available for 72% (140/194) and LIC for 32% (62/194). At enrollment, 48% (70/147) had iron overload as defined by ferritin and/or current chelation. Using the LIC criterion, iron overload had been present at some point in 86% (95/110) of patients. Ferritin positively correlated with LIC (n=45); r=0.62, p3 mg/g DW. Baseline characteristics in patients with and without iron overload are shown in the Table. Notably, even in patients that were never regularly transfused and had a hemoglobin (Hb) >8.7 g/dl, the prevalence of iron overload was 26% (8/31). The frequency of iron overload was significantly higher in patients who had a prior splenectomy (p Data on cardiac iron status was available for 66 patients.Only 2 had cardiac iron overload (defined as T2* Of the 194 patients, 52 (27%) were from the Pennsylvania Amish community. These patients were managed differently than the non-Amish, in that only 2% of the Amish patients were on iron chelation therapy in the 12 months prior to enrollment compared with 43% among the non-Amish cohort. In addition, the Amish had a significant higher prevalence of splenectomy (96% vs 52%, p Conclusion: Iron overload is a common, serious complication in PKD, regardless of age, disease severity, or transfusion status. Although ferritin correlates with LIC for the PKD population overall, at the individual patient level, ferritin is not a good predictor of LIC and a ferritin Disclosures Barcellini: Agios: Consultancy. Neufeld:Novartis: Consultancy. Morton:Agios Pharmaceuticals: Research Funding. Yaish:Octapharma: Other: Study investigator. Kuo:Agios Pharmaceuticals, Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees; Alexion: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Apotex: Other: unrestricted educational grant; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Thompson:bluebird bio: Consultancy, Research Funding; Eli Lily: Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Mast: Research Funding; Baxalta (now part of Shire): Research Funding; ApoPharma: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Research Funding; Amgen: Research Funding. Grace:Agios Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding.

Background: PKD is the most common enzyme defect of the glycolytic pathway causing hereditary non-spherocytic chronic hemolytic anemia. PKD is transmitted as an autosomal recessive trait, caused by both homozygous and compound heterozygote mutations in the PKLR gene, and is characterized by molecular heterogeneity with > 200 different mutations reported. Aim: To describe the PKLR genotypes in the PKD NHS with an in depth characterization of 20 newly reported mutations. Methods: Participants (pts) were enrolled in the PKD NHS, a prospective international study open at 23 sites in North America and Europe. Pts with prior PKLR gene sequencing were not resequenced. DNA from all other pts was extracted and the PKLR gene analyzed by Sanger sequencing at 1 of 2 central labs. All new missense mutations affected highly conserved residues in multiple domains of the PKLR gene, were not detected in 1000 genomes and LOVD database, and were considered pathogenic by NCBI and/or UniProtKB and by Polyphen analysis. Results: Genotype information was available on 140 enrolled pts. Of these, 66 (47%) were related to other subjects enrolled in the study. Molecular characterization confirmed the wide heterogeneity of PKD with 65 different mutations identified, including: 42 missense, 20 disruptive mutations (7 splicing, 6 frameshift, 3 stop codons, and 4 large deletions), 2 inframe insertion/deletions, and 1 promoter variant. Sixty-six pts were homozygous, of whom 55 were of Amish origin carrying the p.R479H mutation. Of the 55, 46 had been transfusion dependent prior to splenectomy and 9 had only received transfusions for acute stressors; 93% had been splenectomized, and all were transfusion independent post-splenectomy. Thirty-nine cases had 2 different missense mutations; 18 had one missense and one disruptive mutation, and 16 had 2 disruptive mutations; 1 patient with 17% residual PK activity displayed 3 different mutations (R510W, E241X and V276WXfs45). Besides R479H, the most common mutations were: R510W (16% of the mutated alleles), R486W (12%), and G241X (9%). Frequencies of R510W and R486W were less than those reported in Europe (41% and 30%, respectively). Twenty mutations, all affecting the PK structural domains, have not been previously described: 14 missense, 3 splicing (c.966(-9) a>g; c.1116(+2) t>c; c.375(+1) g>a), 1 frameshift (R40R fsX7), 1 inframe insertion of 2 amino acids, and 1 large deletion spanning intron 2 to intron 3 (Table). The 3 new splice site mutations were predicted to affect normal splicing when analyzed by HSF3.0, using both HSF and MaxEnt algorithms; in particular, homozygous c.966(-9) a>g was detected in a patient with moderate anemia, reticulocytosis, and mental retardation of unclear etiology. The two new missense mutations detected at a homozygous level (A137V and N156G) were associated with moderate or severe anemia and need for regular transfusions. The latter is located in the Aβ3 catalytic domain/K binding site and probably affects the catalytic efficiency of the enzyme. All the remaining new variants were detected in compound heterozygosity making it difficult to predict their effect on clinical phenotype. Intra-family clinical variability was observed; no correlation was found among the kinds of mutations and the residual PK activity. Conclusion: The molecular features of the largest international cohort of PKD pts are described, including a report of 20 new mutations, thus confirming the wide heterogeneity of the molecular genotype in PKD. Figure 1. Figure 1. Disclosures Morton: Agios: Honoraria, Membership on an entity's Board of Directors or advisory committees. Eber:Agios: Honoraria, Membership on an entity's Board of Directors or advisory committees. Yaish:Agios: Membership on an entity's Board of Directors or advisory committees. Nottage:Janssen Pharmaceuticals: Employment. Kuo:Novartis Canada: Honoraria, Membership on an entity's Board of Directors or advisory committees; Alexion: Honoraria, Membership on an entity's Board of Directors or advisory committees. Grace:Agios: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.

Hereditary spherocytosis (HS) is a genetically and phenotypically heterogeneous hemolytic anemia caused by deficiency in red blood cell (RBC) cytoskeleton proteins leading to disruptions in the vertical association of the cytoskeleton with the RBC lipid bilayer. Monoallelic mutations in the genes encoding ankyrin (ANK1), beta-spectrin (SPTB) and band 3 (SLC4A1) or biallelic mutations in the genes encoding alpha-spectrin (SPTA1), ankyrin, and protein 4.2 (EPB42) result in HS. Autosomal recessive HS due to compound heterozygous defects in SPTA1 is typically severe and diagnosis based on phenotypic assays like RBC morphology, osmotic fragility or ektacytometry is complicated by transfusion dependence resulting in most of the circulating RBCs to be of donor origin. We have developed a rapid comprehensive next-generation sequencing-based assay that evaluates 27 genes with published disease-causing mutations for RBC cytoskeletal disorders, enzymopathies, and CDAs. We describe here patients with hemolytic anemia due to SPTA1 mutations, identified utilizing this assay, and their phenotype-genotype correlation. Each of these cases, when possible, has been also evaluated with ektacytometry and immunoblotting of RBC ghosts for alpha-spectrin quantitation. Wichterle et al in 1996 had estimated that alphaLEPRA(Low Expression PRAgue) mutation (c.4339-99C>T) occurs in SPTA1 gene in about 5% of Caucasians. This mutation leads to activation of an alternate acceptor splice site at position -70 of intron 30, causing frame shift and premature termination, thereby leading to decrease in alpha-spectrin production in this allele to about 16% of normal. We have found a cohort of three transfusion-dependent hereditary hemolytic anemia cases where a nonsense mutation in SPTA1 gene has occurred in trans to alphaLEPRA mutation, resulting in premature termination (see Table 1). Transfusion dependence was alleviated in two of these patients after splenectomy; the third one did not have splenectomy yet. RBC phenotype explored after splenectomy revealed an ektacytometry curve indicating spherocytosis (Figure 1A) and severely decreased alpha-spectrin on immunoblotting along with significant decrease of the associated beta-spectrin (Figure 1B). A patient with moderately severe form of HS, maintaining a hemoglobin value greater than 7 g/dL and requiring only occasional transfusions during periods of illness or stress, was found to have alphaLEPRA occurring in trans to an intronic splicing mutation c.1351-1G>TG where there is substitution at nucleotide-1 of intron positioned between nucleotides 1350 and 1351 of the SPTA1 mRNA. This splicing mutation may allow for some expression of functional alpha-spectrin protein from this allele in contrast to no protein expression in the previous cases of premature termination. Alternatively, other gene mutations, not identified by the next-generation sequencing panel we used, may contribute to this patient's milder phenotype. A couple with history of two fetal losses associated with hydrops fetalis seeked genetic counseling and gave consent to have diagnostic evaluation of genes associated with non-immune hemolytic anemia using targeted next-generation sequencing. Results of the panel revealed a heterozygous frameshift SPTA1 mutation in each of the parents (c.4206delG in the father and c.4180delT in the mother). These mutations in compound heterozygous state in the offspring likely caused total absence of alpha spectrin and fatal hemolytic anemia by the time of birth. Hereditary Spherocytosis is characterized by wide phenotypic variability that will be better understood with studies of genotype-phenotype association. While complete absence of alpha-spectrin expression due to null mutations of both SPTA1 alleles is incompatible with life, a nonsense or splicing SPTA1 mutation in trans to an alphaLEPRA low expression allele causes severe or moderately severe recessive HS, respectively. Targeted next-generation sequencing can be an effective diagnostic tool particularly for patients requiring frequent transfusions that preclude meaningful phenotypical testing of their red blood cells. Figure 1. SPTA1 null mutations occurring in trans to alpha-LEPRA causing severe HS Figure 1. SPTA1 null mutations occurring in trans to alpha-LEPRA causing severe HS Figure 2. Figure 2. Disclosures Begtrup: GeneDx: Employment.

Transcranial Doppler (TCD) screening in children with sickle cell anemia (SCA) identifies abnormally elevated cerebral artery flow velocities that confer an elevated risk for primary stroke. Chronic transfusions offer effective stroke prophylaxis in this setting, but must be continued indefinitely and lead to transfusional iron overload. An alternative treatment strategy that offers similar effective protection against primary stroke, and provides control of iron overload, is needed. TCD With Transfusions Changing to Hydroxyurea (TWiTCH, NCT01425307) was an NHLBI-funded Phase III multicenter randomized clinical trial comparing 24-months of standard treatment (transfusions) to alternative treatment (hydroxyurea) in children with SCA and abnormal TCD velocities. All eligible children had received at least 12 months of transfusions. TWiTCH had a non-inferiority trial design; the primary study endpoint was the 24-month TCD velocity obtained from a linear mixed model, controlling for baseline (enrollment) values, with a non-inferiority margin of 15 cm/sec. The transfusion arm maintained children at HbS 240 cm/sec. Exit brain MRI/MRA exams documented no new parenchymal abnormalities but one child (transfusion arm) developed new vasculopathy. Sickle cell related serious adverse events were more common in the hydroxyurea arm than the transfusion arm (23 to 15), but none was related to study treatment or study procedures. Iron overload improved more in the hydroxyurea arm than in the transfusion arm, with a greater average change in serum ferritin (-1085 compared to -38 ng/mL, p Disclosures Ware: Eli Lilly: Other: DSMB membership; Bayer Pharmaceuticals: Consultancy; Bristol Myers Squibb: Research Funding; Biomedomics: Research Funding. Off Label Use: Hydroxyurea for children with SCA. Owen:Novartis: Speakers Bureau. Rogers:BioRad Labs: Consultancy; Apopharma: Consultancy; Baxter: Consultancy; Glaxo Smith Kline: Consultancy. Kwiatkowski:Shire Pharmaceuticals and Sideris Pharmaceuticals: Consultancy; Sideris Pharmaceuticals: Consultancy; Novartis: Research Funding; ISIS: Membership on an entity's Board of Directors or advisory committees. Heeney:Sancillio: Consultancy; Eli Lilly: Research Funding. Nottage:Janssen Pharmaceuticals: Employment. Cohen:Novartis: Consultancy; ApoPharma: Other: DSMB member.

Background: An international, multicenter registry was established to collect clinical data on patients with PKD, the most common glycolytic defect causing congenital non-spherocytic hemolytic anemia. Aim: To describe and categorize the phenotypic spectrum of PKD, including the range of lab parameters, management, and complications. Methods: 144 patients enrolled on the PKD NHS at 23 sites from 3/2014 to 6/2015. For this report, baseline and retrospective data were included. PKD patients were categorized into 4 severity groups (Gp1-Gp4), with increasing severity of the disease: Gp1. Never regularly transfused +/- prior acute transfusions; Gp2. Regular transfusions prior to splenectomy, post-splenectomy baseline hemoglobin (hb) >8.7 g/dl; Gp3. Regular transfusions prior to splenectomy, post-splenectomy baseline hb ≤8.7 g/dl; and Gp4. Post-splenectomy and currently regularly transfused. To reduce the risk of chance associations when dividing the cohort by phenotype, the cohort was divided into a test set (n=73) to define the categories and a subsequent validation set (n=71). Results: Median age at enrollment was 19.9 years (0.1-70.7) with 47% males. This cohort was 95% Caucasian and 38% Amish. Perinatal complications were frequently reported including preterm birth (33%), perinatal transfusions (35%), and hydrops (10%). Newborn jaundice was common, requiring phototherapy (91%) and/or exchange transfusion (46%). 68% (98/144) had undergone splenectomy at a median age of 3.1 years (0.6-28.1). Common indications for splenectomy included reducing transfusion burden, improving anemia, and enhancing quality of life. The median pre-splenectomy hb was 7.0 g/dl (4.5-12.5). Splenectomy reduced the transfusion burden in 91%. Triggers for hemolysis included: pregnancy (59%), infections (61%), stress (35%), and medications (6%). In the 37% (53/144) who required a cholecystectomy, the median age was 14 years (2.6-60.4) and 35 (66%) occurred post-splenectomy. In both the test and validation cohorts, increased severity was associated with a younger age at diagnosis (p Gp4 pts required regular transfusions even after splenectomy (11/98). In this group, the median age of splenectomy was 5.0 y (2.1-11.8). Ferritin was higher in those who had a splenectomy, even after adjusting for transfusion status (p4 mg/g dry weight and 9/11 (82%) had ferritin >500 ng/ml. Chelation was used in 35 patients at a median age of 11.8 years (1-53.7) with a median ferritin 815 ng/ml (182-5630) and median LIC 5.7 mg/g dry weight (1.7-46.0). Conclusions: This NHS cohort is the largest assembly of PKD patients to date. We defined 4 severity Groups, based on transfusion history, anemia, and splenectomy status. Complications (e.g. iron overload) correlate with disease severity but also occur in milder phenotypes. Based on these findings, regular monitoring of iron status and screening for gallstones should be considered. Transfusion dependence persisted despite splenectomy in 11% of patients. Prospective data from the NHS will provide guidance for monitoring and treatment in this rare anemia. Figure 1. Figure 1. Disclosures Grace: Agios: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Morton:Agios: Honoraria, Membership on an entity's Board of Directors or advisory committees. Eber:Agios: Honoraria, Membership on an entity's Board of Directors or advisory committees. Yaish:Agios: Membership on an entity's Board of Directors or advisory committees. Nottage:Janssen Pharmaceuticals: Employment. Kuo:Alexion: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis Canada: Honoraria, Membership on an entity's Board of Directors or advisory committees. Neufeld:Agios: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Introduction: Sickle cell disease (SCD) is a chronic disease that can cause significant complications including acute chest syndrome, recurrent pain and stroke. Current guidelines for the use of chronic transfusions include primary and secondary prevention of stroke. Although there is currently limited support for the routine use of transfusions for acute vaso-occlusive crisis (VOC), there has been increasing use of chronic transfusions as an alternative treatment for recurrent VOC. Moreover, there is evidence that patients on chronic transfusions have less VOC. We sought to review the outcomes of patients at our institution placed on chronic transfusions for non-stroke related indications. Methods: We performed a retrospective cohort study to summarize clinical and nonclinical features of sickle cell patients on transfusions for non-stroke related complications. Demographic, clinical, and laboratory information were summarized. Acute care events per month were calculated for both the year prior and up to one year following initiation of chronic transfusions. Acute care events were defined as emergency department visits or hospitalization. Results: Of the 378 patients with SCD treated in the pediatric specialty clinic, there were 21 patients being either chronically transfused or exchange transfused. Six (20%) of these patients were initiated on chronic blood transfusions (CBT) for recurrent pain crisis (median age = 12, range 8 to 17). One of these patients also had suspected hepatic sequestration. All patients were type SS and had been treated with hydroxyurea (HU) for an average length of 6.5 years (range 1 to 12 years) at a mean dose of 25 mg/kg (SD 4) prior to initiation of CBT. All patients continued on HU during chronic blood transfusions. Patients were on chronic transfusions for a median of 11 months (range 3 to 58 months) with mean %S while on transfusions of 39.6% (SD 10). Patients were transfused on average every 5 weeks (range 4 to 6 weeks). Following initiation of transfusions, 50% were started on chelation based on criteria of having a ferritin >1000 ng/mL. Mean peak ferritin was not significantly increased in the year following the start of CBT (513 ng/mL ± 343 vs. 1260 ± 934, p=0.13). There was one new alloantibodies (anti-Jk) reported following initiation of CBT, which developed within 3 months. Acute care visits per month were significantly higher in the year prior as compared to after initiation of chronic blood transfusions (1.04 ± 0.45 vs. 0.28 ± 0.22, respectively; p=0.006) (Figure 1). Discussion: We found that patients started on chronic transfusions for pain crisis had a non-significant increase in peak ferritin and a significant reduction in acute care visits. Prior to CBT, all patients had been initiated on hydroxurea (mean dose of 25mg/kg) in an attempt to treat recurrent VOC. However, following therapy for an average of 6.5 years, patients were placed on CBT to prevent further acute care visits and reduce morbidity. All patients were continued on HU while on CBT with no dose adjustment or effort to titrate to maximum tolerated dose. While on CBT, patients had a mean %S of 40%, which is higher than the recommended goal of 30% for stroke related indications. Importantly, despite the higher mean %S, there was a drastic and significant decrease in acute care visits. It should be noted that although only three patients (50%) of patients were placed on chelation, the remaining three had been on transfusions for less than or equal to 6 months and likely to require chelation with continued therapy. The expected elevated ferritin highlights the difficulty in long-term treatment with chronic transfusion and risk for eventual iron overload. The balance between the clinical benefit and potential long-term complications leads to individual assessment of the risks and benefits prior to initiation of chronic transfusions for VOC. These results advocate for the use of prospective studies to evaluate the role for chronic transfusions for non-stroke related indications in SCD. Figure 1 Figure 1. Disclosures Shah: Novartis: Speakers Bureau.

Abstract 1004 Hydroxyurea (HU) is approved for use in adults with Sickle Cell Disease (SCD) and increases the production of fetal hemoglobin (HbF). Increased HbF is associated with decreased clinical severity in adults and children with SCD, such as decreased numbers of vaso-occlusive events, transfusions, and hospitalizations. Higher HbF at initiation of HU is predictive of HbF response, but association between age of hydroxyurea initiation and HbF response has not been investigated. We hypothesize that starting hydroxyurea at an early age may improve hematological and clinical response. In order to determine if younger age at hydroxyurea initiation affects the percentage of HbF achieved with hydroxyurea, we conducted a retrospective cohort study. We identified subjects enrolled in the Duke University Medical Center Comprehensive Sickle Cell program who initiated hydroxyurea when they were less than 17.99 years of age and were prescribed hydroxyurea for at least six months. The following data were abstracted from the medical record between December 1996 and April 2011: age, hemoglobin, percentage HbF, and mean corpuscular volume (MCV) at start of HU and at maximum tolerated dose (MTD) of HU therapy. The correlation coefficient and p-values for various parameters were calculated. Seventy-three patients (41 males and 32 females) were included in the analysis. The mean age at hydroxyurea initiation was 5.5 years (1.2–14.1). The mean hydroxyurea dose at MTD was 28.6 ± 3.2 mg/kg/day. At initiation, the mean hemoglobin was 8.2 ± 1.2 g/dL, the mean MCV was 83±7.4 fl and mean HbF was 10 ± 5.7%. At MTD, the mean hemoglobin was 9.4 ± 1.1 g/dL, the mean MCV was 99 ± 11.1 fl, and the mean HbF was 21.7 ± 9.4%. As expected, at MTD, an elevated MCV was correlated with elevated fetal hemoglobin (r2= 0.19, p= 0.0001) [Table 1]. There was a statistically significant relationship between the age at HU initiation and the HbF at MTD (r2= 0.08, p= 0.015) [Figure 1] as well as the age at HU initiation and the hemoglobin at MTD (r2= 0.19, p= 0.016). The relationship between the age at starting HU and the overall change in HbF (DHbF) was not statistically significant (r2= 0.01, p= 0.41). There was not a statistically significant relationship between age at HU initiation and the MTD of HU (r2= 0.003, p= 0.61). The 6 patients started on HU at age less than 2 years (mean 1.5 ± 0.3 years) maintained a mean elevated HbF of 19.1 ± 5% at last documented follow-up with follow-up ranging from 1.4–13 year of uninterrupted hydroxyurea use. Starting hydroxyurea therapy at a younger age appears to improve HbF response as measured at MTD, although there is variability in the level of fetal hemoglobin attained. There is not an association seen with the DHbF or dose at MTD and age at hydroxyurea initiation. In summary, starting hydroxyurea at a younger age, when HbF is >20%, leads to persistence of HbF production and overall improvement in hematological efficacy. This was not simply the result of achieving MTD at a younger age before physiologic decline of HbF. Disclosures: Off Label Use: Hydroxyurea for complications of sickle cell disease in pediatrics. Shah:Eisai: Research Funding; Adventrx: Consultancy.

Abstract 270 The use of transcranial Doppler ultrasound (TCD), a non-invasive imaging technique, is now clearly established for detecting high risk of stroke in children with sickle cell anemia (SCA). Children with TCD flow velocities ≥200 cm/s have a 10% risk of primary stroke per year. For these children, chronic blood transfusions (CBT) are recommended and have been shown to reduce the risk of primary stroke by up to 90%. The incidence of stroke has decreased to 0.06–0.17 per 100 patient-years since the institution of TCD screening (Fullerton et al. Blood 2004; Enningul-Egham et al., J Pediatr 2010). Although patients with conditional TCDs (flow velocities 170–199 cm/s) have an estimated stroke risk of 2–5% annually, and their rate of conversion from conditional to abnormal is 23% over an 18 month period (Hankins JS et al., BJH 2008), there are no clinical guidelines for primary stroke prevention in this group. We previously conducted a prospective cohort study of hydroxyurea in 37 children with SCA and TCD velocities >140 cm/sec, and demonstrated that TCD velocities decreased significantly after starting hydroxyurea (Zimmerman et al., Blood 2007; NCT00402480). In order to determine if hydroxyurea provided sustained reductions in TCD velocities, we conducted a retrospective review of these 37 children in this original cohort who had elevated TCD velocities and long-term hydroxyurea treatment. The following data were abstracted from the medical record between April 2000 and September 2009: treatment with hydroxyurea and CBT; adherence with treatments; stroke and non-stroke neurological events; and TCD time-averaged mean velocities (TAMV) immediately prior to initiation of hydroxyurea and at the end of extended follow-up. The primary outcome was comparison of pre and post TCD TAMV using a paired t-test. The mean age of enrollment on the original study was 6.8 years (1.8-14.8) and the mean age at follow-up was 12.9 years (5.3-18.5). The mean follow-up was 5.8 years (0.8-8.5) with an overall follow up of 215.1 patient years. Twenty males and 17 females were enrolled. The mean hydroxyurea dose was 25.2 ± 5.6 mg/kg/day, with one patient discontinuing therapy after 15 months. At follow-up, the mean hemoglobin was 8.9 ± 1.2 g/dL and mean HbF was 16 ± 7.2%. Sustained decreases were observed in both the right MCA (164.8 ± 25.5 cm/s to 124.9 ± 35 cm/s, p Disclosures: Off Label Use: Hydroxyurea is used to reduce complications of sickle cell anemia.

Abstract 1649 INTRODUCTION: Implantable venous access devices (VADs) are used in sickle cell disease (SCD) for patients with poor venous access to facilitate chronic blood transfusions and management of acute complications. Children and adults with chronic illnesses have high rates of VAD-related complications including bloodstream infection and thrombosis. Patients with SCD may be at higher risk given the presence of functional asplenia and evidence of a hypercoaguable state. The objective of this study was to define the frequency of VAD related bloodstream infections and thrombosis in adults and children with SCD. PATIENTS AND METHODS: We performed a single institution retrospective review of VAD placement in patients with SCD. Subjects were identified through the sickle cell clinic database and the Hospital Information System. Subjects were included if they had SCD, VAD placement between December 1, 1998 to December 1, 2009 and had completed at least 12 months of follow-up. VAD-related bloodstream infection was defined by positive blood culture and VAD-related thrombosis (deep vein thrombosis, superior vena cava syndrome, and pulmonary embolism without lower extremity thrombosis) was defined by imaging. Comparisons were made between pediatric and adult sickle cell patients using Student's t-test for continuous variables and Fisher's exact test was used to compare categorical variables; p RESULTS: Of the greater than 800 sickle cell patients followed at our Comprehensive Sickle Cell Center, 32 subjects were eligible for inclusion (median age 20 years, range 1–59). There were 81 VAD placed (median 2.6 VAD per patient, range 1–7) with a total of 49268 catheter days (median 608, range 323–3999). The mean catheter lifespan in adults (1798 days ± 266) was significantly higher than pediatric patients (971 ± 328, p=0.039). There were a total of 66 VAD-related bloodstream infections (1.34 infections per 1000 catheter days) occurring in 17 of 32 (53%) subjects. Although not statistically significant, children had fewer VAD-related bloodstream infections (3 of 10; 30%) compared to adults (14 of 22; 64%, p=0.08). There were 24 catheter-related thromboses (0.49 thromboses per 1000 catheter days) occurring in 10 of 32 (41%) of subjects. Children also had fewer VAD-related thrombosis (1 of 10; 10%) compared to adults (9 of 22; 40%, p=0.08). The overall rates of infection and thrombosis per 1000 catheter days were not significantly different between adult and pediatric patients. CONCLUSION: In summary, we report a long lifespan and low rate of infection in the subjects who had VADs during the study period. Most concerning was a high proportion of adults with catheter-related thrombosis, which adds the burden of anticoagulation to patient management and put patients at risk for post-thrombotic syndrome. Potential lifespan of VADs, risk of bloodstream infection and thrombosis as well as its long-term consequences should be discussed with patients and families considering VAD placement. Disclosures: No relevant conflicts of interest to declare.